The present invention relates to a novel indicator for gauging the condition of solid propellant within a rocket motor and providing a visible display indicative of the approach of the end of the service life of the motor.
In a solid propellant rocket engine, the propellant is contained within the combustion chamber of the engine in solid form. The physical mass or body of the propellant, referred to as the grain, may take on a variety of configurations defining an internal surface geometry to aid in even, controlled burning of the propellant in the operation of the rocket engine. The solid propellant normally contains all the constituents necessary for sustaining fuel combustion to provide thrust, and conventionally comprises a mixture of constituents including an oxidizer such as a nitrate or perchlorate, a fuel matrix such as an organic resin, plastic, or rubber, and additives, stabilizers, and inhibitors to facilitate propellant grain fabrication, to control grain burning rate, to preserve physical and chemical stability, and to retard propellant grain deterioration in storage. By reason of their chemical composition and physical configuration, solid propellant grains may be stored for considerable periods of time and made available for use without substantial preparation as compared to other rocket engine propellant types, such as those comprising liquid cryogens.
Most solid propellants are sensitive to variations in ambient temperature and humidity, the grains having a tendency to soften on hot days and embrittle on cold days. It may therefore be necessary to restrict the ambient temperature range over which the rocket is deemed operable, depending on the particular propellant composition, and to monitor and control the temperature and moisture conditions under which the fueled rocket, or the propellant grain material separately, should be stored, particularly for rocket engines required to be maintained in a state of operational readiness for substantial periods of time. However, practical limits exist as to the frequency and thoroughness of inspection and the degree of environmental protection which can be accorded rocket motors within tactical weapons deployed in the field. Further, life cycles of individual air-launched missiles powered by the rocket motors may vary according to environmental conditions encountered on multiple flights on which the missiles are carried.
The present invention provides a reliable visual dosimeter for use with a solid propellant rocket motor to indicate the shelf life or, more accurately, the approach of the end of the service life of a solid propellant fueled rocket motor. The capsule of the present invention comprises an expandable metal container including a sample of the propellant used in the rocket motor, but with a slightly smaller concentration of chemical stabilizer than that included in the rocket motor propellant composition. The capsule is disposed at a suitable location within the casing of the rocket near the motor so that the capsule is exposed to substantially similar thermal and other environmental conditions as that to which the propellant of the motor is exposed. By reason of the somewhat lower concentration of chemical stabilizer in the sample, the sample decomposes at a predictably faster rate than the rocket motor propellant composition. Gaseous products of the decomposition of the sample expand the metal container of the dosimeter capsule, which in an expanded condition is conspicuous by its color and protrusion, thereby providing by analogy an indication of the condition of the solid propellant in the rocket motor. The capsule therefore may provide an effective measure of the approach of the end of the service life of the rocket motor. Substantial improvement in operational reliability of solid propellant rocket engines may therefore be provided through use of the invention described herein.
It is, therefore, a principal object of the present invention to provide a dosimeter for indicating the condition of the solid propellant of a rocket motor.
It is a further object of the invention to provide a dosimeter capsule disposable within the casing of a rocket or the like for indicating the approach of the end of the service life of a solid propellant rocket motor.
It is yet a further object of the invention to provide a dosimeter capsule for providing a quick, thorough and reliable indication of the condition of a solid propellant rocket motor in storage.
These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.